Copper surface-alloying of H2-permeable Pd-based membrane for integration in Fischer–Tropsch synthesis reactors

Abstract

Self-supported palladium tubular membranes are surface-functionalized and tested for the selective and controlled addition of H2 along a fixed-bed catalytic reactor for Fischer–Tropsch hydrocarbon synthesis (FTS). In order to avoid CO poisoning of the active sites of the metallic membrane at low working temperatures (~250 °C), a Cu-based protective layer is deposited on the outer surface of a tubular membrane by RF sputtering at room temperature. Upon thermal treatment in H2, the Cu layer alloys with Pd on the membrane surface, as confirmed by means of XRD, FESEM and TEM, while the membrane assembly is fully functional, i.e. the negative effect of CO surface adsorption is highly diminished and the membrane provides an appropriate H2 flux (e.g. 12 ml/min·cm2) under the harsh operation conditions practiced in FT synthesis. When the Cu-functionalized membrane is fully integrated in the FTS reactor (250 °C, 20 bar, 30% CO in feed), the membrane delivers a stable H2 permeation flux and enables to increase the yield of hydrocarbons in the range of gasoline (C5–C12) while reducing methane formation over a bifunctional CoRu/Al2O3-zeolite catalyst.